This invention relates generally to static convergence assemblies for cathode ray tubes (CRTs) and particularly to a static convergence assembly wherein a plurality of magnetic elements are maintained in fixed angular orientation relative to one another and are independently adjustable with regard to distance from, and orientation with respect to, the neck of a CRT.
In color television receivers, color images are produced on the screen of a CRT through the combined use of three independent electron beams and an array of red, green and blue phosphor dots on the screen surface. Color images of various hues are produced through controlled independent illumination of the primary color phosphor dots. To this end, color CRTs include a shadow mask which functions to assure that individual phosphor dots will be illuminated only by those electrons which arrive from a particular direction. Since the paths of the three electron beams generated within the tube are different from one another, the CRT, when properly constructed and adjusted, can be operated such that each beam illuminates only those phosphor dots of a particular color. When each of the beams is modulated with appropriate information, a wide spectrum of perceived colors can be displayed.
To generate the three electron beams, color CRTs are typically provided with three electron guns arranged in either a straight "in-line" or triangular "delta" pattern. Regardless of the pattern employed, proper operation of the CRT results when the three electron beams are made to converge toward a single point on the shadow mask. To provide such convergence, a variety of devices have been developed which seek to provide independent control of the static position of each electron beam.
In one prior convergence device, a plurality of generally circular rings, carrying a number of magnetic pole pairs, were disposed around the neck of the CRT. The rings were grouped into pairs which could be independently rotated around the CRT neck in unison or in opposition to one another. Although this convergence device was effective in operation, it was difficult to construct and adjust and, therefore, had a detrimental effect on manufacturing econony.
In another prior convergence device, a number of parallel, straight, ferrite rods, each having a plurality of pole pairs formed thereon, were mounted in tangential orientation relative to the neck of a CRT. Each of the rods was adjustable with respect to its axial and rotational position such that beam convergence could be readily achieved. Although this convergence device was considerably simpler in both operation and construction than earlier devices, it nevertheless retained some complexity and thus offered room for still further improvement.
In view of the foregoing, it is an object of the present invention to provide a new and improved CRT static convergence assembly.
It is a further object of the present invention to provide a CRT static convergence assembly which is simple and economical to manufacture and adjust, and which provides effective adjustment of beam convergence.
It is still another object of the present invention to provide a CRT static convergence assembly which is adaptable for use with both "in-line" and "delta" electron gun configurations.